Probiotics 101: What CFUs and Strains Mean
A probiotic label reads a little like a lab notebook — genus, species, a strain code, and a CFU count. None of it is decorative. Each part identifies something specific about what's actually in the product.
Genus, species, and strain
A probiotic name like "Lactobacillus acidophilus LA88" has three parts. "Lactobacillus" is the genus — a broad category. "acidophilus" is the species — more specific, but still describes a whole family of related microorganisms. "LA88" is the strain — the actual specific, individually identified microorganism used in that product. This matters because research on probiotics is generally strain-specific: findings about one strain of a species don't automatically apply to a different strain of the same species, even though they share a genus and species name. A label that names the full strain, not just the species, is giving you more identifiable information than one that stops at "Lactobacillus acidophilus."
What a CFU is
CFU stands for Colony-Forming Unit — a way of counting viable (living, able to reproduce) microorganisms, based on how many visible colonies they form when cultured in a lab. A probiotic label's CFU count is a measure of quantity — how many live organisms of that strain are present — not a measure of a specific strain's characteristics or effects. Counts are often given in the billions per serving, which sounds dramatic mostly because these organisms are microscopic; billions of them still amount to a very small mass.
Multi-strain blends
Some products combine several distinct strains — sometimes even from the same species — into one blend, on the idea that different strains may play different roles. When a label lists a "Probiotic Blend" with a combined weight rather than individual amounts, that follows the same proprietary-blend disclosure rules as any other blended ingredient — see our guide on understanding proprietary blends for how that labeling works generally.
Viability and storage
Because probiotics are living organisms, viability (the share that are actually still alive and able to colonize) can decline over time and is affected by storage conditions — heat and moisture in particular. A CFU count on the label typically refers to the count at time of manufacture, unless the label specifically states an "at expiration" guarantee. Following a product's stated storage instructions is part of what keeps that original count meaningful by the time you actually take it.